NADPH-specific glutamate dehydrogenase in Chlorella is inducible by addition of ammonium to previously uninduced synchronous cells, at any time during its cell cycle. The initial rate of induced enzyme accumulation increases in S-phase in proportion to the increase in gene dosage. In synchronous cells growing in the continuous presence of inducer, the expression of newly replicated genes of this enzyme is delayed until after S-phase. Removal of inducer results in the very rapid decay (t1/2 equals 10 min) of enzyme activity. The objectives are to characterize the molecular mechanisms regulating the change in induced enzyme activity during induction and deinduction and the delay between gene replication and gene expression in synchronous cells cultured in continuous presence of inducer. Specific immunological and biochemical procedures will be used in measurements of the rates of induced enzyme synthesis and degradation, in the quantitation to total translatable mRNA of the enzyme in vitro translation systems, and in an indirect immunoprecipitation procedure for isolation and purification of the specific mRNA. cDNA will be made from mRNA used in hybridization studies to quantify the total mRNA sequences of the enzyme in different cellular fractions and to measure the NADP-GDH gene dosage during the cell cycle.